Hydrometallurgical processing system with hydrostatic pressure assisted autoclaving

ABSTRACT

The hydrostatic pressure differential existing in a column of fluent material conveyed through an excavated passage possessing a downward entrance run and upward return run facilitates hydrometallugical processing including metals recovery and treatment of ores. Conveyance of the fluent material through the passage is facilitated by appropriate means including a difference in elevation between the inlet and outlet and/or gaseous expansion applied proximate the bottom of the return run. Cooling of effluent proximate the outlet may be utilized consequent to application of heat during processing as in roasting ore. The passage is excavated through rock fully capable of containing the pressures anticipated and has an interior casing which seals the rock porosity. Iron reinforced concrete is recommended in appropriate wall thicknesses. Location of appropriate pipe lines for pressurized fluid additives including compressed gas and liquid chemical reagents and the location of electrical lines if utilized within this interior casing is also recommended. Continuous operation autoclaving of hydrometallurgical processes in a safe and economical manner is facilitated.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to hydrometallugical processing, more specifically to hydrometallurgical processing under pressure, and most specifically to hydrometallugical processing under hydrostatic pressure.

[0003] 2. General Discussion of the Prior Art

[0004] It is considered that elevated pressures and temperatures may facilitate various hydrometallurgical processes and that conventional autoclaves, entirely unsuited to hydrometallurgical processing, are also known that are characterized by construction above ground in a manner capable of maintaining elevated pressures and temperatures inside an autoclave chamber. This requires a structure resisting all the considerable tensile forces exerted by the internal autoclave chamber pressure outward and otherwise opposed only by ambient pressure upon the exterior of the structure.

[0005] The housing of an autoclave localizes high pressure and temperature in a limited volume which must be isolated from the immediate environment for safety to personnel. Autoclave housings are typically manufactured from very durable, expensive, alloys based on stainless steel and titanium. Pursuit of metallurgical processing resistance to both extremely aggressive chemical reagents and extremely abrasive materials in processing would require utilization of special alloys inclusive of chromium, nickel, and molybdenum which can reliably withstand the combined action of high pressure and temperature, mechanical abrasion, and chemical aggression. No known steel or titanium alloys are reliably resistant to some highly effective chemical reagents such as chloride. Sealing the various lines involved for using a conventional autoclave system for hydrometallurgical processing is considered problematic with regard to safety and operational costs. All of the connections of all the lines from the pumps and compressors and to the chamber(s) along with associated valves, gauges, et cetera, must be sealed and the seals renewed periodically because these seals will wear quickly. These factors are considered to render conventional known autoclaves generally unsuited to many hydrometallurgical processes wherein continuous processing of a slurry is desirable.

[0006] It is considered that a conventional autoclave possesses a chamber which is charged, locked, pressurized, processed, depressurized, and discharged. Operation in an economically continuous manner would require, with conventional technology, an extremely sophisticated system for the pressurization of the fluent material with simultaneous introduction of material at ambient pressure and temperature and removal of material at ambient pressure and temperature. In practical terms staging is required in which pressurization, processing, and depressurization are conducted in sequence either in a single chamber or in several chambers through which the material is conveyed through pressure locks which can withstand elevated pressures and temperatures and which system would necessarily require alternate cycling of elevated and ambient pressures and temperatures within a structure which is strong enough to resist the force of the interior pressure against the ambient pressure upon the structure exterior. Agitation of slurry is also desirable and this imposes another complication as does the typical necessity of cooling the effluent in addition to depressurization.

[0007] The use of conventional autoclave technology for hydrometallurgical processing is consequently considered problematic and inherently constrained in a manner which effectively prohibits continuous, economic operation, in addition to requiring a physical structure of such strength and complexity as to render the same impractically expensive.

Statement of Need

[0008] Because autoclaving of fluent material during hydrometallurgical processes requires staging in order to achieve pressurization, processing, and depressurization a truly continuous system is considered problematic and the attempt to provide a facsimile of continuous operation consequently expensive with regard to the equipment required, maintenance, and operation. A poignant need is therefore discerned for continuous autoclaving in hydrometallurgical processing which avoids the expense of facilitating pressurization cycles in a closed chamber and which avoids the expense of external structure which resists the force of the elevated interior pressure outward against the ambient pressure upon the exterior of the structure.

SUMMARY OF THE INVENTION Objects of the Invention

[0009] The encompassing object of the present invention is the provision of a system for autoclaving during hydrometallurgical processing that is inherently less expensive than conventional systems.

[0010] A primary object of the present invention is the provision of a system for autoclaving during hydrometallurgical processing that is inherently less expensive in operation than conventional systems.

[0011] A first auxiliary object of the present invention is the provision of a system for autoclaving during hydrometallurgical processing that avoids alternate pressurization cycling of a chamber.

[0012] A first ancillary object of the present invention is the provision of a system for autoclaving during hydrometallurgical processing that facilitates continuous operation.

[0013] A second ancillary object of the present invention is the provision of a system for autoclaving during hydrometallurgical processing that facilitates continuous operation and is simple with regard to required equipment.

[0014] Another primary object of the present invention is the provision of a system for autoclaving during hydrometallurgical processing that is inherently less expensive in installation expense than conventional systems.

[0015] A second auxiliary object of the present invention is the provision of a system for autoclaving during hydrometallurgical processing that obviates the expense for a structure capable of safely withstanding pressures elevated from ambient.

[0016] A third auxiliary object of the present invention is the provision of a system for autoclaving during hydrometallurgical processing that obviates the expense for a structure capable of safely withstanding temperatures elevated from ambient.

[0017] A third ancillary object of the present invention is the provision of a system for autoclaving during hydrometallurgical processing that minimizes the expense of the ancillary equipment required, particularly equipment required for conveying slurry and facilitating pressurization cycles.

Principles Relating to the Present Invention

[0018] In achievement of the above stated objects it is suggested that a continuous operation autoclave for hydrometallurgical processing which furthermore obviates the expense of the structure required as well as the expense of operation may be obtained with an excavated passage possessing a downward entrance run and an upward return run. The runs may be vertical or inclined and may have various processing stations appropriately located therealong but an excavated passage facilitates the elevated pressures desired for autoclaving. The passage contains an inlet and an outlet and an elevational difference between the two may be utilized to convey fluid or fluent material, particularly slurry introduced through the inlet through the passage and out the outlet or to assist in conveyance which is otherwise assisted.

[0019] The use of compressed gas, especially air in what is known in the field as an airlift, is specifically suggested whereby the gas is compressed to a pressure above the hydrostatic pressure at the depth concerned and expelled into the slurry somewhere along the return run, preferably at the bottom of a vertical run. The gas so released is buoyant and rises in the return run thereby reducing the density of the slurry therein and propelling the fluent material up the return run. Alternatively or additionally, pressure may be increased at the inlet of the passage with the use of a conventional pump. The use of a pump is preferably minimized because slurry of the type primarily addressed herein is often extremely abrasive and consequently quite offensive to the interior surfaces of a pump contacting the same. The minimization of the use of a pump for impelling flow of the slurry, moreover, allows processing of a relatively thick slurry without the expense associated with using multiple pumps. A compressor for air release toward the bottom of the return run capable of propelling slurry flow of a given rate is considered less expensive than utilizing another pump for this because the slurry is both abrasive and generally incompressible while air is both relatively unabrasive and quite compressible.

[0020] It is also recommended that a hyposometricaly resultant elevational head with respect to the inlet and outlet be utilized to convey the slurry through the passage preferably in conjunction with the use of compressed air released proximate the bottom of the return run and/or the use of a pump at the inlet to create a pressure differential with respect to the outlet all of which constitute means of inducing flow of the slurry through the passage and hence the autoclave which is in contrast to the use of multiple pumps for a conventional, above ground, system. A system in accordance with the principles relating to the present invention is inherently facilitative of continuous flow induced by various means and is inherently benefited by the depth of the excavation which determines the pressure naturally achieved and maintained by hydrostatic pressure during autoclaving. This enables a considerable reduction in the cost of a structure capable of withstanding the force of the pressure differential between the elevated pressure required of autoclaving and ambient pressure by using surrounding rock as a part of the structure. Excavation also substantially reduces the cost of a structure capable of safely withstanding the temperatures required of processing as the surrounding rock effectively insulates the autoclave from human exposure to the same. Cooling of the effluent prior to exposure above ground, if desired, is readily achieved with a cold water heat exchanger located toward the top of the return run.

[0021] This requires however, even in the case of excavating the passage through solid rock, that the interior surface created by excavation be sealed. Ferro-reinforced concrete is recommended for the construction of an interior casing to the passage. Depending upon the particular characteristics of the autoclaving processes desired various thicknesses ranging from one half to two feet are recommended for a concrete interior casing and a casing head of greater thickness is suggested in certain cases wherein elevated temperatures and/or pressures proximate the inlet or outlet are anticipated. It is further suggested that pipe lines for the compressed air and other compressed gases or liquids utilized in processing be run through this casing which must withstand the pressures anticipated in compression against the surrounding rock but which need not withstand these pressures in tension as in the case of a conventional autoclave structure above ground. Steel must be utilized throughout in a conventional structure while a system in accordance with the principles relating to the present invention may use relatively inexpensive materials including ferro-reinforced concrete for the casing and silica based ceramic for a lining sealing the interior surface of the casing in a preferred embodiment in accordance with said principles.

[0022] In addition to achieving a continuous operation which is very economic the cost of the installation is hence also reduced considerably in comparison with conventional autoclaving as the cost of a ceramic lined concrete casing is considerably less than an equivalently sized steel structure and while the costs of excavation must be incurred the total cost for a system in accordance with the principles relating to the present invention is considered to be a fraction of the cost of using conventional hydrometallurgical processes in possessing an equivalent capacity. While compressors, pumps, and heating apparatus are desired for some of the hydrometallurgical processes encompassed the simplicity of the basic system obviates the need for all the equipment required for cyclic pressurization of an autoclave chamber as well as the vast majority of the equipment associated with conveyance of slurry and agitation of the same during processing.

[0023] Most importantly, the structure and equipment required to create and maintain pressure in a conventional autoclave is considerably reduced by appropriate utilization of the hydrostatic pressure available in a fluidic column of sufficient depth. The apparatus otherwise required to develop and maintain this pressure as well as the apparatus required to facilitate cyclic pressurization of a chamber in autoclaving is wholly obviated. The equipment required for continuous operation is considerably diminished and simplified and large rates of processing thereby facilitated with an inherently simple, reliable, and safe system. Other benefits and advantages to be derived from the practical application of the principles relating to the present invention in fulfillment of said principles may be appreciated with a reading of the detailed discussion below of the preferred embodiments, especially if made with reference to the drawings attached hereto briefly described immediately below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a vertical plane cross sectional schematic view of a system in accordance with the principles relating to the present invention suited to the processing of ores containing precious metals with cyanidation utilizing separate shafts for the entrance and return runs.

[0025]FIG. 2 is a vertical plane cross sectional schematic view of a system in accordance with the principles relating to the present invention suited to the processing of sulphide concentrates and ores with high sulphide content utilizing separate shafts for the entrance and return runs.

[0026]FIG. 3 is a vertical plane cross sectional schematic view of a system in accordance with the principles relating to the present invention suited to the recovery of metals using hydrogenation in processing and utilizing a single shaft for adjacent entrance and return runs.

[0027]FIG. 4 is a vertical plane cross sectional schematic view of a system in accordance with the principles relating to the present invention utilizing a single shaft for concentric entrance and return runs.

[0028]FIG. 5 is a vertical plane cross sectional schematic view of a system in accordance with the principles relating to the present invention utilizing a several shafts for one entrance and two return runs.

[0029]10 wet slurry

[0030]11 inlet

[0031]12 entrance run

[0032]13 autoclave area

[0033]15 gaseous addition

[0034]16 liquid addition

[0035]17 addition lines

[0036]19 casing

[0037]20 effluent

[0038]21 outlet

[0039]22 return run

[0040]23 bottom of passage

[0041]25 air release

[0042]26 exhaust air

[0043]27 air lines

[0044]29 lining

[0045]30 compressor

[0046]31 pump

[0047]32 connecting run

[0048]33 rock

[0049]35 oxygen

[0050]36 reagents

[0051]37 natural gas

[0052]39 hydrogen

[0053]50 gaseous slurry

[0054]51 roast chamber

[0055]52 water addition

[0056]53 condensation area

[0057]55 cold water supply

[0058]56 heat exchanger

[0059]59 dry slurry

[0060]60 liquid solution

[0061]61 inlet pipe

[0062]62 exhaust pipe

[0063]63 heating area

[0064]65 heating element

[0065]66 relief valve

[0066]67 electric lines

[0067]69 casing head

[0068]70 pressure lock

[0069]71 high pressure pump

[0070]72 check valve

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0071] FIGS. 1-5 depict a preferred embodiment of the principles relating to the present invention wherein a fluidic material inclusive of: a wet slurry 10, one resulting from condensation of a gaseous slurry 50, and a liquid solution 60; is conveyed in continuous flow through an excavated passage including an autoclave area 13 between at least one inlet 11 and at least one outlet 21 which comprise, respectively, openings of the passage at the top of an entrance run 12 and a return run 22 in communication with each other and possibly connected by an intermediary connecting run 32 all of which is sealed with respect to the surrounding rock 33 by a continuous internal casing 19. The autoclave area 13 is determined by the presence of elevated pressure including hydrostatic pressure obtaining at a given depth that possesses a linear relation to depth and is also a simple product of density which two factors, absent any additional pressurization, determine pressure elevation above ambient, and whereby the bottom of the excavated passage has the maximum pressure.

[0072] A difference in elevation hypsometrically between the inlet 11 and the outlet 21 may be utilized to convey fluidic material including a wet slurry 10 or liquid solution 60 simply poured at ambient pressure into the inlet 11 down the entrance run 12 and up through the return run 22 out the outlet 21 if the elevation of the inlet 11 is of sufficient elevation above the outlet 21. Alternatively or additionally to this hypsometric elevational head it is recommended, especially for a wet slurry 10, that a compressed air release 25 in the return run 22 preferably near the bottom 23 of the same as depicted in FIGS. 1 & 2 be utilized to propel flow of the wet slurry 10 upward through the return run 22 and out the outlet 21. A pump 31 may also be utilized to convey the fluidic material through the passage, preferably located upon the inlet 11 as depicted in FIGS. 1-3.

[0073] It has been recommended that the casing 19 be constructed from ferro-reinforced concrete of a substantial thickness and that gaseous addition 15 and liquid addition 16 of reagents utilized in the hydrometallurgical processing be supplied through addition lines 17 run through the casing 19 which is preferably poured into a suitable mold after disposition of these addition lines 17. Compressors 30 and pumps 31 are of further utility for supply of gaseous addition 15 and liquid addition 16 of chemical reagents through the addition lines 17 as the hydrostatic pressure at the level of addition must be exceeded and the resulting injection may further be directed downward in the entrance run 12 to impart motive energy in the desired flow direction and will result in agitation of the wet slurry 10, gaseous slurry 50, or liquid solution 60 regardless of the direction of the addition. The volume rates of gaseous and liquid addition 15, 16 or reagent are further preferably variable so that the same may be coordinated with the rate of flow through the excavated passage in optimization of the hydrometallurgical processing resulting in the desired effluent 20 at the outlet 21.

[0074] It is preferred, regardless of the specific hydrometallurgical processing performed, that an embodiment of the principles relating to the present invention possess a lining 29 of the passage bonded to the casing 19 which is further preferably comprised of acid resistant ceramic, based on silica or synthetic materials. With the preferred ferro-reinforced concrete construction casing 19 an appropriate ceramic lining 29 is easily bonded thereto and, since both materials possess similar, linear, heat expansion coefficients, thermal deformation is avoided and fracturing between the lining 29 and casing 19 obviated. This is considered of great importance to useful operational life of a given system. A silica or synthetic based ceramic lining 29 is highly resistant to chemically aggressive environments including chloride, saturated HCl, NaOCl, Cl₂, and FeCl₃.

[0075] It is also noted that, regardless of the intended use, both the entrance run 12 and the return run 22 must be inclined from horizontal, that a substantially vertical orientation is generally preferred, and that therefore the ground area required is minimized which, in combination with the inherent isolation against elevated pressures and temperatures provided by excavation downward into rock 33, enables a reduction of ground area required for a processing plant in accordance with the principles relating to the present invention in comparison with conventional technology of equivalent capacity by over ninety per cent.

[0076] With regard to more particular hydrometallurgical processes several examples are discussed below with direct reference to FIGS. 1-3 respectively.

EXAMPLE 1 Hydrometallurgical Processing of Gold Bearing Ores by Cyanidation

[0077] With reference to FIG. 1 an excavated passage possessing an entrance run 12 which is approximately twice the width of the return run 22 but of approximately equivalent breadth, or dimension into the drawing sheet, is considered. A maximum depth at the bottom 23 of the excavated passage of approximately one hundred meters is suggested. With an arbitrary breadth of one meter and widths of two and one meters respectively for the entrance and return runs 12, 22 the total volume of the passage is three hundred cubic meters with the return run 22 possessing half the volume of the entrance run 12. With a wet slurry density of 1.5 tons per cubic meter the hydrostatic pressure varies across the depths of twenty to one hundred meters from two to ten atmospheres or approximately thirty to one hundred fifty psig. A compressed air release 25 is provided at the bottom 23 of the passage which is also the bottom of a substantially vertical return run 22 supplied through an air line 27 which is preferably supplied by a compressor 30. An associated accumulator and valving are not shown but are simply presumed in conventional utilization.

[0078] Gold bearing ore, preferably in an aqueous wet slurry 10, is fed through a pipe 61 through the casing head 69 at the top of the entrance run 12. This introduction of wet slurry 10 through this inlet 11 is preferably pressurized and use of a pump 31 as depicted in FIG. 1 is suggested. Gaseous addition 15 from a pressurized supply of oxygen 35 is made as depicted along with liquid addition 16 from a pressurized supply of reagents 36 including cyanide solution. And gaseous addition 15 of compressed air is also made in the entrance run 12 as depicted beginning at about ten meters depth down to about twenty-five or thirty meters depth at five meter intervals while the gaseous additions 15 and liquid additions 16 of oxygen and cyanide solution, respectively, are made in eight to ten meter intervals from about thirty-five meters of depth down to ninety to ninety-five meters of depth. The addition lines 17 for the cyanide solution especially require corrosion resistant construction.

[0079] Active aeration of the aqueous wet slurry 10 bearing gold ore by the gaseous addition 15 in the upper portion of the entrance run 12 partially oxidizes the surfaces of minerals therein such as sulphides and carbonaceous materials which prevents reaction of the same with cyanide further downstream. Exhaust air 26 escapes to ambient through an exhaust pipe 62 through the casing head 69 located at the top of the entrance run 12. The use of a relief valve, not shown, upon the exhaust pipe 62 is suggested to maintain a pressure differential between the top of the entrance run 12 and ambient. This exhaust air 26 is devoid of toxic components.

[0080] The aerated wet slurry 10 bearing gold ore flows downward into the autoclave 13 area in the lower portion of the entrance run 12 where gaseous and liquid additions 15, 16 are made as discussed above and further preferably including active carbon in suspension and in stoichiometric proportions with the oxygen and cyanide appropriate to the hydrostatic pressure of the depth of the addition. Proportions are readily adjusted by pressure modification in accordance with monitoring conducted with measuring devices mounted within the casing 19 exposed to the wet slurry 10 flowing thereby induced largely by the airlift provided by the compressed air release 25 proximate the bottom 23 of the substantially vertical return run 22 and propelled upwards through the same out the outlet 21 after which the processed effluent 20 goes through a separator, not shown, wherein compressed air and active carbon are extracted and the resultant effluent 20 then neutralized in recovery of the gold.

[0081] The central chemical reaction to this example can be described by the following formula:

2Au+4NaCN+O₂+2H₂O=2Na[Au(CN)₂]+2NaOH+H₂O₂.

[0082] The speed of the process effecting this chemical reaction is typically restricted by the amount of dissolved oxygen in the solution: aqueous wet slurry 10 or pulp. The natural solubility of oxygen in cyanide solutions is 39 milligrams per liter at standard temperature and pressure (STP): 25° C. and 1 bar. The range of cyanide concentration anticipated in solution 60 is 0.03-0.05%. In accordance with stoichiometric proportion determined by the formula above the optimal oxygen concentration in solution 60 is hence 30-50 milligrams per liter. In large scale industry ore processing air is used instead of pure oxygen 35 for economic reasons. Air is 21% oxygen and at STP has 8.2 milligrams of oxygen per liter, less than a quarter of the optimal concentration. Pulp recirculation combined with aeration and agitation are commonly used to achieve complete extraction of the gold in solution. The process duration for a given amount of solution is essentially prolonged while air is added. The efficiency of the extraction is hence clearly restricted as demonstrated by conventional practice which compensates for sub-optimal oxygen concentrations with recirculation of the pulp combined with aeration and agitation.

[0083] Increased rates of gold extraction for the same wet slurry 10 by this process can only be effected by increasing the speed of the chemical reaction given above. The optimal rate of reaction is achieved with stochiometric proportions. This is achieved with the principles relating to the present invention by increasing the oxygen levels in solution to the optimal oxygen concentration of 30-50 milligrams per liter with hydrostatic pressure of 4.5-4.8 bars in the autoclave area 13. At a depth of 30 meters the hydrostatic pressure in the fluent column having a density of 1.5-1.6 grams per cubic centimeter is 4.5-4.8 bars and this depth of 30 meters is hence recognized as a threshold depth for achieving optimal gold extraction rates with preferred embodiment of the principles relating to the present invention for hydrometallurgical processing of gold bearing ore.

EXAMPLE 2 Hydrometallurgical Processing of Sulphide Concentrates and Ores

[0084] With reference to FIG. 2 entrance and return runs 12, 22 separated from each other by a few meters or more are considered. This is in contrast to Example 1 wherein the two runs 12, 22 are seen to be substantially adjacent if in separately excavated shafts, and in sharp contrast to the examples depicted in FIGS. 3 & 4, wherein directly adjacent and concentric arrangements, respectively, occupying the same excavated shaft are depicted. In contrast to the rectangular cross sections of the passage described above in Example 1, a circular cross section possessing an area of one to two square meters is suggested.

[0085] The entrance run 12, moreover, is seen to be comprised of three different areas: a roast chamber 51 in an upper portion, a condensation area 53 therebelow, and an autoclave area 13 below both. The lower end of the entrance run 12 is joined to the lower end of the return run 22 by a connecting run 32 which is preferably inclined downward as seen and of a similar cross sectional area as the return run 22 which is 20-30% less than that utilized for the entrance run 12 with the exception of the constriction between the roast chamber 51 and the condensation area 53 and the inlet 11 which is preferably comprised of an inlet pipe 61 as depicted through which crushed and otherwise prepared ore material is supplied under pressure to the roast chamber 51.

[0086] The casing head 69 through which the inlet pipe 61 runs is preferably five to eight meters thick to provide proper isolation. Sulphide material in a dry slurry 59 is added under pressure and oxidized in the roast chamber 51 at a depth of twenty to thirty meters while considerable heat is applied, preferably by burning natural gas with the addition of compressed oxygen as shown wherein gaseous addition 15 from a pressurized supply of oxygen 35 and a pressurized supply of natural gas 37 is made in appropriate proportions and quantity to maintain a temperature in the roast chamber 51 of approximately 450-550 degrees Celsius. The resulting gaseous slurry 50 containing SO₂ and SO₃ flows into a condensation chamber 53 wherein cold water addition 52 is made from a pressurized cold water supply 55 to form sulphuric acid and reduce the temperature to 200-250 degrees Celsius with a commensurate increase in density. Further cold water addition 52 converts the gaseous slurry 50 into a liquid wet slurry 10 which is the state flowing into the autoclave area 13 where gaseous addition 15 from a pressurized supply of oxygen 35 is made and the hydrometallurgical processes completed with the sulphuric acid created from the gaseous SO₂ and SO₃ which conversion prevents escape of these toxic gases into the atmosphere. The maximum depth suggested is 150-200 meters.

[0087] It is recommended, as seen in FIG. 2, that a conventional heat exchanger 56 be located in the return run 22 proximate the outlet 21 to reduce the temperature of the effluent 20 and that an open air exhaust 26 be located above the outlet 21. The effluent 20 is cooled by water run through the heat exchanger 56 which is seen to have a cold water supply 55 and a hot water return 57 after which the effluent 20 flows out the outlet 21 for separation and recovery of the hydrometallurgically processed materials.

[0088] A number of hydrometallurgical processes involve the participation of gaseous agents wherein the rate of reaction is optimized by increased temperature and pressure. Efficient oxidation in the leaching of sulphides of Cu, Zn, Ni, and Fe are all enabled under conditions of high pressure and temperature. For the majority of sulphides minimally economic hydrometallurgical processing can be achieved with approximately 120° C. and 4-5 bars of pressure. For CuFeS₂ 135° C. and 6 bars pressure is recommended while only 105° C. and 3 bars pressure is recommended for Fe₈S₉. Average values of 120° C. and 4-5 bars pressure are hence observed. A minimum depth of 30 meters provides the autoclave area 13 with about 4.5 bars of pressure with a slurry density of 1.3-1.5 grams per cubic centimeter and this minimum depth is hence considered a threshold value for economic processing of sulphide bearing ores in accordance with the principles relating to the present invention.

EXAMPLE 3 Hydrometallurgical Processing Utilizing Hydrogen in Metals Recovery from Solution

[0089] With reference to FIG. 3 an excavated passage possessing a suggested maximum depth of 300-350 meters and cross sectional area of approximately four fifths to one meter squared is considered. The entrance run 12 is of moderately larger cross sectional area than the cross sectional area of the return run 22 and both may be rectangular with the two separated only by the casing 19 therebetween so that only a single shaft is excavated. The casing 19 possesses a silica based, acid resistant, thermo resistant, lining 29 as does an inlet pipe 61, which preferably possesses a cross sectional area of between three and six tenths of a square meter, through which filtered metal bearing solution 60 including, as examples, CuSo₄ or NiSo₄, are fed under pressure preferably provided by a high pressure pump 71.

[0090] Gaseous addition 15 from a pressurized supply of hydrogen 39 is made, as seen in FIG. 3, along virtually all of both entrance and return runs 12, 22. This is preferably done, as seen, with an addition line 17 running down through the casing 19 between the two runs 12, 22. In this example it is desired to maintain relatively high pressures throughout the system and pressure locks 70 are therefore located upon both the inlet 11 and outlet 21 at the top of the casing head 69 at the top of the two runs 12, 22. The pressure lock 70 upon the inlet 11 may be provided by a check valve 72 permitting flow only in one direction downline of a high pressure pump 71 while a relief valve 66 which opens in accordance with increased pressure will regulate outflow of the effluent 20 to an expansion chamber and collector 73 which may further comprise a condenser and which separates gaseous exhaust 76 from the liquid effluent 20. The metal recovered therefrom is in the form of a powder suspended in the effluent 20. The pressure locks 70 ensure maintenance of a relatively high pressure throughout the system by permitting only high pressure fluid inflow through the inlet 11 and pressurized outflow through the outlet 22.

[0091] Pressure in the upper portion of the entrance run 12 is further elevated in consequence to heat added in the heating area 63 which is preferably performed, as seen in FIG. 3, with use of an electric heating element 65 which is supplied with electricity through electric lines 67. The desired temperature here is approximately 170-200 degrees Celsius. A heat exchanger 56, preferably of the cold water type discussed above and located at the upper portion of the return run 22 as depicted in FIG. 2, is also considered desirable. The pressurized, filtered, metal bearing solution 60 is first heated and then saturated with hydrogen which is supplied essentially throughout the processing to achieve stoichiometric proportion with the rate of hydrogen consumption in the ongoing reactions.

[0092] This particular hydrometallurgical processing therefore utilizes most of the entrance run 12 and return run 22 as an autoclave area 13. It is noted that the hydrogenation reactions promoted thereby essentially benefit from higher pressurization and both the relatively great depth and maintenance of relatively high pressure throughout the system are intended to provide an economic system which is highly efficient. 2500-3500 cubic meters per day is considered an optimal rate of hydrometallurgical processing in this example.

[0093] In further, more technically detailed example, recovery of copper from aqueous solution 60 of CuSO₄ is given by the following formula:

CuSO₄+H₂=Cu⁰+H₂SO₄.

[0094] As in the previous example of treating gold bearing ores with cyanide, the effectiveness of the chemical process depends upon the concentration and solubility of the gaseous component, in this case hydrogen 39 rather than oxygen 35. At 100° C. and pressure of 1 bar the solubility of gaseous hydrogen is only 0.4 milligrams per liter.

[0095] Typical copper concentrations in solution during recovery possess a range of 40-60 grams per liter. The stoichiometrically corresponding concentration of hydrogen is 1.3-2 grams per liter. At atmospheric pressure and 100° C. with recirculation and addition of gaseous hydrogen and agitation the reaction is completed in 3,200-3,500 cycles taking 80-120 hours.

[0096] In accordance with the principles relating to the present invention, with a minimum depth of 30 meters in the autoclave area 13 and average hydrostatic pressure of 4.5 bars, the solubility of gaseous hydrogen in solution is increased to 8.1 milligrams per liter. Combined with an increase also in temperature to 140° C. the same reaction is completed in only 20-250 cycles, less than ten per cent of the cycling time required by conventional methods. In this example the slurry density is 1.4-1.5 grams per liter and the hydrostatic pressure at 30 meters is 4.2-4.5 bars.

[0097] Optimal recovery rates for metals such as copper and nickel, moreover, are achieved with temperatures of 150-180° C. and a depth for the autoclave area 13 of at least 100 meters. The above defined reactions for recovery of copper are completed in only 15-20 minutes under these optimal conditions and recirculation is clearly unnecessary.

[0098] The above three examples discussed relative to FIGS. 1-3 are each considered to be characterized by a particular type of hydrometallurgical processing which is considered to benefit from the application of elevated pressures and temperatures during the same and which illustrate in a practical context the advantages to be gained with fulfillment of the principles relating to the present invention. While each example is particularized with regard to the system embodying said principles and the actual hydrometallurgical processes defined suggest the system characteristics described above and recognized as desirable for each type of processing. Each type of processing, moreover, is recognized as exemplifying a larger range of more specific processes according to the combination of metals being recovered, the ore available, the concentrations of sulphide and other relevant materials, et cetera.

[0099] It is mentioned in this vein that the definition of a metal ore itself is considered dependent upon whether the metal(s) therein can be “commercially extracted”:

[0100] ORE. A metal-bearing mineral from which a metal or metallic compound can be extracted commercially. Earths and rocks containing metals that cannot be extracted at a profit are not rated as ores. Ores are named according to their leading useful metals. The ores may be oxides, sulfides, halides, or oxygen salts. A few metals also occur native in veins in the minerals. Ores are usually crushed and separated and concentrated from the guague with which they are associated, and then shipped as concentrates based on a definite metal or metal oxide content. The metal content to make an ore commercial varies widely with the current price of the metal, and also with the content of other metals present in the ore. Normally, a sulfide copper ore should have 1.5% copper in the unconcentrated ore but, if gold or silver is present, an ore with much less copper is workable, or, if the deposit can be handled by high-production methods, a mineral of very low metal content can be utilized as ore. (Materials Handbook, 13th Edition, Brady & Clauser, McGRAW-HILL Inc., 1991, page 586).

[0101] It is hence considered that the processing of ores, which is a primary intention of the principles relating to the present invention, is often complicated by the presence of multiple metals in varying concentrations and secondly that the number of metals present in a given ore which are economically recoverable may be increased, or a lower quality ore made viable, “if the deposit can be handled by high-production methods”. It is considered that this observation more precisely touches on the larger significance of the present invention: hydrometallurgical processing in a continuous, economic, manner using an excavated passage autoclave area 13 enables commercial processing of ores which otherwise would not be commercially viable. The use of hydrostatic pressure generated by depth in a fluidic column maintained by a casing 19 with an appropriate lining 29 in compression against the surrounding rock 33 provides for continuous flow autoclaving and elevated temperature processing in a manner which is inherently less expensive and safer than a structure built above ground.

[0102] It is thus considered that the present invention is very widely applicable to ores and processing that have hitherto been considered commercially unviable and encompasses applications well beyond the few particular examples described herein which are intended to encompass all presently known hydrometallurgical processing with respect to metals recovery from ore.

[0103] In each of the examples detailed above with relation to FIGS. 1-3 it has, for instance, been considered advantageous to utilize a pump 31, with one example utilizing a high pressure pump 71, at the inlet 11 for the introduction of a wet slurry 10, dry slurry 59, or solution 60. Earlier it was stated that obviation of equipment including pumps, particularly if processing a slurry 10, 59, was considered an advantage gained with an embodiment in accordance with the principles relating to the present invention. This is considered to be the case even if a pump 31 or even a high pressure pump 71 is utilized because the pressures in the autoclave area 13 are still increased by hydrostatic pressure and are elevated much higher than would be possible with the equivalent pump in a conventional system built above ground.

[0104] While in the case of hydrometallurgical processing using hydrogen in metals recovery from solution 60 a high pressure pump 71 is recommended for obtaining elevated pressures throughout the system. A conventional pump 31 is utilized with slurry 10, 59 primarily as the most practical means available for providing a high rate of flow of material to be processed through the inlet 11. In the example involving introduction of a dry slurry 59 particularly, the type of processing addressed requires pressurization at the inlet 11 because the roast chamber 51, in which the first step in processing is conducted, by nature of its operation creates considerable pressure. Any embodiment in fulfillment of the principles relating to the present invention utilizes an excavated passage with an inlet 11 and an outlet 21 and while the difference in elevation between the two may be utilized to impel flow therethrough and compressed air release 25 toward the bottom of the return run 22 impels flow through the same, the application of pressure upon the inlet 11 to create a pressure differential between it and the outlet 21 still provides a very useful means for increasing the rate of flow through the autoclave area 13.

[0105] The embodiments depicted in FIGS. 4 & 5 are not related to any particular hydrometallurgical process but are intended to further illustrate the principles relating to the present invention. The embodiments depicted in FIGS. 1-3 each utilized one entrance run 12 and one return run 22 essentially parallel and adjacent to each other. In one example the two runs 12, 22 are fairly close, in another deliberately separated, and in the third directly adjacent. In the first two examples two different shafts are required along with a connecting run 32 while in the last only a single shaft is utilized. In FIG. 4 this variation is extended into use of concentric entrance and return runs 12, 22. A pump 31 is utilized to supply solution 60 under pressure to a centrally disposed entrance run 12 which is surrounded by a casing 19 which has a lining 29 on both sides with the return run 22 being concentrically external within a larger diameter casing 19. The outlet 21 is located at a modest elevational decrease from the inlet 11 and is open to ambient pressure. The pressure differential between the inlet 11 and the outlet 21 created by the pump 31 is the primary motive force impelling flow through the system.

[0106] In FIG. 5 multiple return runs 22 are depicted further distinguished over the previous examples by relatively modest and inconsistent inclination upwards from horizontal rather than the substantially straight vertical disposition characterizing previous examples. Also, the only force impelling flow is hypsometical and a naturally occurring geological formation is exploited to provide a considerable elevational difference between the inlet 11 and the outlets 21. This embodiment is considered illustrative of possible retrofitting of existing mine shafts which are frequently connected and which, in following veins of quality ore, often radiate outward from the bottom 23 of a central, substantially vertical, excavated shaft which in this case provides the entrance run 12 while two connected shafts provide two connected return runs 22. Liquid addition 16 is also gravity fed through an addition line 17 located at the inlet 11. The autoclave area 13 is comprised mainly of the lower reaches of the return runs 22 but also includes the lower portion of the entrance run 21. 

It is emphasized that the foregoing is intended to provide one skilled in the art with what is considered the best manner of making and utilizing a system in accordance with the principles relating to the present invention and is not to be construed in any manner as restrictive of the scope of said invention nor of the rights and privileges obtained by Letters Patent for which we claim:
 1. An autoclave system for conducting various processes in which fluent material, inclusive of solids, liquids, and gases, is subjected to pressure elevated from ambient, said system comprising: an excavated passage, flow inducing means, and fluid addition means; said excavated passage possessing an entrance run with an inlet and a return run with an outlet, each said run possessing an inclination from horizontal and extending downward through rock, both said runs possessing communication with each other at a predetermined depth of at least thirty meters with respect to said inlet and said outlet, said entrance run and said return run each possessing a fully encompassing continuous casing sealing surrounding rock porosity; said flow inducing means being capable of inducing flow of fluent material introduced through said inlet through said excavated passage, including autoclave areas in which elevated pressure is naturally created and maintained by a hydrostatic column of fluent material of at least thirty meters, and out said outlet; said fluid addition means being capable of adding at least one fluid reagent to at least one location inside said passage at a pressure exceeding the hydrostatic pressure existing at that location in the passage when said passage is filled with fluent material; whereby flow of fluent material introduced through said inlet is induced downward through said entrance run and the addition of fluid reagent under pressure into, and the pressure maintained hydrostatically in, said flow of fluent material facilitates hydrometallurgical processing of said fluent material under elevated pressure resulting in processed effluent outflow through said outlet.
 2. The system of claim 1 wherein said entrance run possesses a volume exceeding the volume of said return run.
 3. The system of claim 2 wherein said entrance run possesses a substantially uniform cross sectional area which exceeds in size a substantially uniform cross sectional area possessed by said return run.
 4. The system of claim 1 wherein said entrance run and said return run both occupy a single excavated shaft.
 5. The system of claim 4 wherein said entrance run and said return run are adjacent and separated by a wall integral to the casing.
 6. The system of claim 4 wherein said entrance run and said return run are concentric and separated by an interior casing concentric with an outer casing.
 7. The system of claim 1 wherein said continuous casing sealing surrounding rock porosity is primarily constructed in ferro-reinforced concrete.
 8. The system of claim 7 wherein said fluid addition means is inclusive of addition lines run through said ferro-reinforced concrete.
 9. The system of claim 7 wherein said continuous casing possesses a ceramic lining.
 10. The system of claim 1 further possessing means of adding heat to an area in said entrance run.
 11. The system of claim 10 further including a heat exchanger located in said return run.
 12. The system of claim 10 wherein said means of adding heat is comprised of an electric heating element.
 13. The system of claim 10 wherein said means of adding heat is comprised of burning gaseous fuel supply in elevation of temperature of the fluent material in a roast chamber.
 14. The system of claim 13 further including a condensation chamber below said roast chamber in which addition of water is made by said fluid addition means.
 15. The system of claim 1 wherein said fluid addition means is capable of adding liquid reagent.
 16. The system of claim 1 wherein said fluid addition means is capable of adding gaseous reagent.
 17. The system of claim 1 wherein said flow inducing means includes an elevational head resulting hypsometrically from said inlet possessing a superior elevation than said outlet.
 18. The system of claim 1 wherein said flow inducing means includes use of compressed air release within said return run as a flow inducing means lifting fluent material upward through said return run.
 19. The system of claim 18 wherein said compressed air release is located proximate a bottom of said return run.
 20. The system of claim 19 wherein said return run above said compressed air release possesses a substantially vertical orientation.
 21. The system of claim 1 wherein said flow inducing means includes a pump providing pressurized introduction of said fluent material.
 22. The system of claim 21 wherein said outlet possesses a pressure elevated from ambient. 